Method and apparatus for modifying the effects of color burst modifications to a video signal

ABSTRACT

In the known color stripe process for preventing recording of video signals, the color burst present on each line of active video is modified so that any subsequent video tape recording of the video signal shows variations in the color fidelity that appear as undesirable bands or stripes of color error. This color stripe process is defeated first by determining the location of the video lines including the color stripe process, either by prior experimentation or by on-line detection. Then some or all of the lines including the modified color bursts are modified so as to render the overall video signal recordable. The modification is accomplished in a number of ways, including phase shifting the color stripe burst into the correct phase, replacing some of the color stripe bursts or a portion of particular color stripe bursts so that they are no longer effective, and mixing the color stripe burst with color stripe signals of the correct phase so as to eliminate most or all of the phase error present. The modified color bursts are defeated, in other versions, by modifying the horizontal sync pulse signals immediately preceding the modified color bursts so that the modified color bursts are not detected by a VCR and hence have no effect.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention pertains to a method and apparatus forprocessing a video signal, and more particularly to removing (defeating)effects of phase modulation of the color burst component of the videosignal.

[0003] 2. Description of the Prior Art

[0004] U.S. Pat. No. 4,577,216, “Method and Apparatus For Processing aVideo Signal,” John O. Ryan, issued Mar. 18, 1986 and incorporated byreference, discloses modifying a color video signal to inhibit themaking of acceptable video recordings thereof. A conventional televisionreceiver produces a normal color picture from the modified signal.However, the resultant color picture from a subsequent video taperecording shows variations in the color fidelity that appear as bands orstripes of color error. Colloquially the modifications are called the“color stripe system” or the “color stripe process”. Commercialembodiments of the teachings of this patent typically limit the numberof video lines per field having the induced color error or colorstripes.

[0005] Color video signals (both in the NTSC and PAL TV systems) includewhat is called a color burst. The color stripe system modifies the colorburst. The suppression of the color subcarrier signal at the TVtransmitter requires that the color TV receiver include (in NTSC) a 3.58MHz oscillator which is used during demodulation to reinsert the colorsubcarrier signal and restore the color signal to its original form.Both the frequency and phase of this reinserted subcarrier signal arecritical for color reproduction. Therefore, it is necessary tosynchronize the color TV receiver's local 3.58 MHz oscillator so thatits frequency and phase are in step with the subcarrier signal at thetransmitter.

[0006] This synchronization is accomplished by transmitting a smallsample of the transmitter's 3.58 MHz subcarrier signal during the backporch interval of the horizontal blanking pulse. FIG. 1A shows onehorizontal blanking interval for color TV. The horizontal sync pulse,the front porch and blanking interval duration are essentially the sameas that for black and white TV. However, during color TV transmission(both broadcast and cable) 8 to 10 cycles of the 3.58 MHz subcarrierthat is to be used as the color sync signal are superimposed on the backporch. This color sync signal is referred to as the “color burst” or“burst”. The color burst peak-to-peak amplitude (40 IRE for NTSC TV asshown) is the same amplitude as the horizontal sync pulse.

[0007]FIG. 1B shows an expanded view of a part of the waveform of FIG.1A including the actual color burst cycles. During the color TV blankingintervals, such a color burst is transmitted following each horizontalsync pulse.

[0008] In one commercial embodiment of the color stripe process, nocolor burst phase (stripe) modification appears in the video lines thathave a color burst signal during the vertical blanking interval. Theseare lines 10 to 21 in an NTSC signal and corresponding lines in a PALsignal. The color stripe modifications occur in bands of four to fivevideo lines of the viewable TV field followed by bands of eight to tenvideo lines without the color stripe modulation. The location of thebands is fixed (“stationary”) field-to-field. This color stripe processhas been found to be quite effective for cable television, especiallywhen combined with the teachings of U.S. Pat. No. 4,631,603 alsoinvented by John O. Ryan and incorporated herein by reference.

[0009] In NTSC TV, the start of color burst is defined by thezero-crossing (positive or negative slope) that precedes the first halfcycle of subcarrier (color burst) that is 50% or greater of the colorburst amplitude. It is to be understood that the color stripe processshifts the phase of the color burst cycles relative to their nominal(correct) position which is shown in FIG. 1B. The phase shifted colorburst is shown in FIG. 1C. The amount of phase shift shown in FIG. 1C is180° (the maximum possible).

[0010] Further, the amount of phase shift in the color stripe processcan vary from e.g. 20° to 180°; the more phase shift, the greater thevisual effect in terms of color shift. In a color stripe process for PALTV, a somewhat greater phase shift (e.g. 40° to 180°) is used to beeffective.

[0011] Other variations of the color stripe process are also possible.

[0012] U.S. Pat. No. 4,626,890, “Method and Apparatus For Removing PhaseModulation From the Color Burst”, John O. Ryan, issued Dec. 2, 1986 andincorporated by reference, discloses removing the phase modulation ofthe U.S. Pat. No. 4,577,216. This removal is useful in eliminating muchof the effects of the process disclosed in U.S. Pat. No. 4,577,216 forrecording.

SUMMARY

[0013] The present inventors have determined that improvements arepossible on the teachings of above mentioned U.S. Pat. No. 4,626,890,especially pertaining to eliminating or reducing the effects of certainvariants as described above of the color stripe process of U.S. Pat. No.4,577,216.

[0014] Thus in accordance with the present invention, a circuit modifiesand/or removes the color stripe process, or modifies the video signal sothe color stripe process is not evident, i.e. has no influence on atelevision set or VCR.

[0015] In one embodiment, the video line locations of the color stripecolor bursts are known. That is, it is known in which video lines thecolor stripe modified bursts occur, as in the above described commercialembodiment of the color stripe process. These locations are stored in apreprogrammed memory which provides signals indicating those videolines. Also, the same preprogrammed memory provides an indication ofwhether the entire color stripe burst or only a part of it is to bemodified.

[0016] A modification circuit which also receives the video signal, anduses the information as to the location of the color stripe bursts,removes and/or modifies the color stripe bursts or otherwise modifiesthe video signal (i.e. modifies the horizontal sync pulse immediatelypreceding the color stripe burst) so that the effect of the color stripeprocess is attenuated or eliminated.

[0017] With regard to the present invention, it has been found that itis not necessary to completely eliminate the color stripe bursts; withtypical commercially available television sets and VCRs, eliminatingsome of the color stripe bursts or attenuating the color stripe burstseither in terms of amplitude or duration, or removing or attenuating aportion of each or most colorstripe bursts, has been found effective toovercome the effect of the color stripe process, allowing a recordable(copiable) video signal to be produced.

[0018] Sometimes the color stripe process is not fixed in line location.Other times, even where it is so fixed, it is not desired or possible toprovide the preprogrammed memory. Then instead a phase detector detects,for each video line, the presence of a color stripe burst, i.e. detectscolor bursts having induced phase modulation. Upon detection of thecolor stripe burst, the modification circuit (as above) modifies eitherthe color burst or other portions of the video signal (i.e. thehorizontal sync pulse) so as to attenuate or eliminate the effect of thecolor stripe burst.

[0019] It is to be understood that correcting or replacing the colorstripe bursts in accordance with the invention does not requirecompletely eliminating the phase shift (modulation); a reduction of thephase shift to some small value (e.g. 5° or less for NTSC) has beenfound to be effective, in that the typical viewer will not perceive theattendant color shift.

[0020] Thus, the present method and apparatus have several embodiments.There are several different methods of determining the location of thecolor stripe burst, either by knowing its location from prior analysisor by actual detection. Various embodiments are also disclosed hereinfor defeating the color stripe process. These, as described above,generally rely on first determining the video line locations of thecolor stripe bursts, either by knowing their location from prioranalysis and programming in the location to e.g. a programmable memory,or by sensing each individual color stripe burst color burst on a videoline-by-line basis. Either of these methods for determining the locationof the color stripe burst may be achieved by various circuits.

[0021] As an alternative, one replaces all color bursts with correctphase bursts, generating the correct bursts by particular circuitsdifferent from that illustrated in Ryan U.S. Pat. No. 4,626,890 asdisclosed below.

[0022] A typical circuit which relies on knowledge of the location ofthe color stripe burst (for the case of the color stripe burst videoline locations being stationary) generates vertical and horizontaltiming signals from the input video signal and from these generatesindicator signals indicating particular video lines in each video fieldand particular portions of the line for which it is desired to provide amodification to the color burst.

[0023] The detector approach typically uses a phase detector whichincludes a subcarrier regeneration circuit such as a phase lock loop,crystal filter or frequency multiplier circuit for determining the phaseof the color burst, and then compares this detected phase to the nominalphase (using a phase comparator) and provides an indicator signal whenthe color stripe burst is present, i.e. when the color burst phase hasbeen modulated to deviate from the normal (correct) phase. Thisindicator signal then controls the desired modification to that line.

[0024] The actual modifications to the video lines to defeat the colorstripe process fall into two main categories. In the first category, thecolor burst itself is altered so as to defeat (eliminate or attenuate)its effect on a typical VCR. In the second category, the horizontal syncpulse immediately preceding a color stripe burst is altered, thuscausing a VCR not to respond to the succeeding color stripe burst.

[0025] The first approach (in which the color stripe burst itself ismodified) may be performed in several ways.

[0026] In one embodiment the color stripe burst is blanked out and notreplaced. Alternatively, the color stripe burst is blanked out and a newcolor burst of correct phase inserted therefor. The color stripe burstalternatively is phase shifted so that it is corrected in phase.

[0027] In another embodiment, the color stripe burst is delayed in timewith respect to the trailing edge of the preceding horizontal syncpulse, so that the color stripe burst occurs outside the detectionwindow of the VCR color burst circuitry.

[0028] In another embodiment, the phase error (shift) present in thecolor stripe burst is measured and a color burst of a negative vectorphase is added thereto, and then the summed color burst may beattenuated to a normal level. In another embodiment, a very largeamplitude color burst of correct phase is added at the color stripeburst location and then the summed color bursts are attenuated to anormal level, thus effectively eliminating the effect of the colorstripe burst. (This can be done on all video lines—those having colorstripe bursts as well as non-color stripe burst lines.)

[0029] In another embodiment, a color burst of inverted phase (oppositeto that of the color stripe burst) is added to substantially null outthe color stripe burst, and then a color burst of correct phase is addedin. In another related embodiment, the correct phase of a normal colorburst is determined and the difference between the phase of that normalcolor burst and the phase of the color stripe burst is measured. Then asignal with a negative phase as to the difference is generated and usedto modify the color stripe burst, to produce color bursts that are“swinging” in phase the same amount of degrees from the correct burst inalternate lines. That is, in an example, the color stripe burst phase is+45°. Then one modifies a sufficient number of TV lines with each colorstripe burst having about half of the color burst having a phase of+90°, while changing the other half of the color burst to have a phaseof −90° (the opposite phase angle). This swinging is averaged out by atypical VCR.

[0030] In another embodiment, all the color bursts of correct phasethroughout the TV field are replaced with color bursts having the phaseof the color stripe bursts or having some (arbitrary) chroma phaseangle. Then the chroma phase of each corresponding TV horizontal line ismodified to match the phase of the color stripe bursts or to be thearbitrary chroma phase angle.

[0031] It is to be understood that in each of these embodiments it hasbeen found that it is not necessary to modify all of a particular colorstripe burst; it has been found that modifying as little as one-half ofa color stripe burst effectively eliminates its effect for a typicalVCR. Also, it has been found that it is not necessary to modify eachcolor stripe burst present in a video field; the typical VCR can make acopiable recording of a signal with as much as one-half of the originalcolor stripe bursts still present for a typical commercial embodiment ofthe color stripe system.

[0032] Another embodiment which involves modifications to the colorstripe burst itself heterodynes the color stripe burst signal into thecorrect phase. One can also use heterodyning to effectively blank outburst as seen by the VCR. This results for instance in heterodyning thecolor stripe burst to a new frequency to which the VCR will benon-responsive, i.e. a frequency substantially higher or substantiallylower than the normal TV subcarrier frequency.

[0033] The other broad category of methods for defeating the colorstripe process uses various modifications to the horizontal sync pulsespreceding at least some locations of the color stripe bursts. If the VCRsync separator fails to sense a horizontal sync pulse, the VCR will notgenerate a burst sampling pulse and hence will not detect any subsequentcolor stripe burst. Thus it has been found that removing the horizontalsync pulse of a color stripe burst line results in a copiable videosignal. Additionally, it has been found that actual removal of thehorizontal sync pulse is not necessary; instead the horizontal syncpulse may be for instance attenuated in width (duration) by narrowing itto the point where the horizontal sync pulse is not detected by thecorresponding sync separator circuitry in the VCR, and hence thesucceeding color stripe burst is also not detected.

[0034] Also, it has been found that removing only some of the horizontalsync pulses coincident with the color stripe bursts reduces theeffectiveness of the color stripe process. Other embodiments formodifying the horizontal sync pulse include DC level shifting upward ofthe horizontal sync pulse, thus causing the VCR sync separator to failto produce an output signal.

[0035] Another embodiment relating to the horizontal sync pulses is toblack clip or amplitude attenuate the horizontal sync pulses so thatthey are not sensed by the VCR's sync separator.

[0036] Another embodiment which also relates to the horizontal syncpulses adds a delay of about 2 microseconds between the trailing edge ofthe horizontal sync pulse and the beginning of the color stripe burst;thus the VCR color burst sampling pulse missamples the delayed colorstripe burst and misses it.

[0037] It is to be understood that while the description hereingenerally refers to NTSC TV, with relatively minor modifications of thetype well known to one of ordinary skill in the art the methods andcircuits described herein are suitable for use with PAL TV, whichsimilar to NTSC TV, has a color burst immediately following a horizontalsync pulse. The major differences between NTSC and PAL television, i.e.the number of lines per field and number of fields per second, are notmaterial to the present invention and is the circuits described hereinmay be readily modified to accommodate PAL TV.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIGS. 1A and 1B show a standard NTSC TV waveform.

[0039]FIG. 1C shows a modification to the waveform of FIG. 1B therebyillustrating the color stripe process.

[0040]FIGS. 2A to 2G show waveforms illustrating various ways ofdefeating the color stripe process in accordance with the invention.

[0041]FIG. 3 shows a block diagram of an apparatus in accordance withthe invention.

[0042]FIGS. 4A to 4C show circuits for generating a correct colorsubcarrier frequency and other signals to defeat the color stripeprocess.

[0043]FIGS. 5A and 5B and 6A and 6B show various circuits to defeat thecolor stripe process.

[0044]FIG. 7 shows a circuit to improve playability, for use withelimination of horizontal sync pulses.

[0045]FIG. 8 shows another circuit to defeat the color stripe process.

[0046]FIG. 9 shows a circuit for subcarrier regeneration.

DETAILED DESCRIPTION

[0047] The following describes a number of embodiments to defeat thecolor stripe process. First is a description relating to waveforms andprocesses; second is a description of various related circuits.

Process Description

[0048] The following are various color stripe defeat processes inaccordance with the invention.

[0049] 1. One or more color burst phase lock loops (or other circuits)are used to find the mean color burst phase and then all color bursts(whether color stripe or not) are replaced throughout the video signal.

[0050] This replacement may be of only a portion of a particular colorburst. For instance, of the standard eight to ten cycles of NTSC colorburst, one may replace e.g. the first five cycles, the last five cycles,or any other group of e.g. four to six cycles. The replaced cycles neednot be consecutive; one may replace alternate cycles, leaving “good”(corrected) cycles interspersed with “bad” (color stripe) cycles. Italso is possible to add corrected color burst cycles outside of theirnormal location and overlying the horizontal sync pulses, since thesewill be detected by a VCR. It is to be understood that the recognitionby the present inventors that only a portion of a particular color burstneed be replaced forms a part of the invention. Moreover, the partialreplacement is also applicable to other of the embodiments describedhereinafter.

[0051] 2. A crystal or horizontal line phase locked loop (or equivalentsuch as a burst crystal filter) supplies a signal whose frequency is a455 or 910 (in NTSC TV) multiple of the horizontal line frequency anddivided down to the color frequency, with phase reset of every fieldbased on odd or even field identification. This color frequency is usedto replace (in the sense described above) all or sufficient of the colorstripe bursts to allow a copiable result.

[0052] 3. A color phase lock loop is used to identify the specifichorizontal video lines that are color striped, and then the color stripeburst is phase shifted (using e.g. a conventional phase shifter circuit)to obtain a usable recording.

[0053] 4. Determine which are the color stripe horizontal lines, andcoincident with these color stripe lines, switches in a phase shiftedcolor burst to replace the color stripe bursts or all bursts.

[0054] 5. Either sense the color stripe video lines (e.g. via a colorphase lock loop) or identify color stripe video lines otherwise anddelay each active video line and thus the chroma so as to provide acopiable signal.

[0055] 6. Either sense the color stripe lines (e.g. via a color phaselock loop) or identify color stripe lines otherwise, and phase shift thechroma in the active lines where the color stripe process is located tomake a copiable color stripe free tape. Phase shifting the chroma isaccomplished by a conventional circuit such as an operational amplifierhaving its inverting terminal connected via a resistor to the inputsignal and its non-inverting terminal connected via a capacitor to theinput signal. The input terminal of its operational amplifier isconnected to the inverting terminal via a resistor, and also a resistorof the same value is connected to the inverting input terminal of theoperational amplifier and its output.

[0056] 7. Locate video lines in which the color stripe bursts occur,then measure the color stripe burst phase error. This is done with aphase detector with the color stripe burst as one input and a colorsubcarrier regeneration circuit (e.g. a color crystal ringing circuit)supplying the second input. Then a color burst of a negative vectorphase is added to correct the burst phase and (in one version) readjustthe burst amplitude to a normal level of e.g. 40 IRE units.

[0057] 8. Locate video lines in which the color stripe bursts occur,then effectively replace the color stripe bursts by adding a very largeamplitude of the correct color burst to the color stripe burst and thenattenuate the resultant summed burst, thus effectively eliminating anyeffect of the incorrect color stripe).

[0058] 9. Replace the color stripe bursts by first locating the colorstripe bursts, then adding color bursts of an inverted phase tosubstantially null out the color stripe bursts and adding in colorbursts of correct phase. This requires ascertaining the phase of thecolor stripe bursts, by observation or by measurement as above. Thisprocess results in replacement of the color stripe bursts, withouthaving to switch the bursts out.

[0059] 10. Use a color frequency phase lock loop (or other method) tofind the correct phase of a normal color burst signal and to find thephase difference between the normal color burst and the color stripeburst signals. Using this information, generate a signal with a negativephase of this difference and use this signal to modify all or part ofthe color stripe burst with the negative phase burst signal to producecolor bursts that are swinging in phase the same amount of degrees fromthe correct burst from one line to the next line or within the portionsof burst in the same lines. A VCR tends to average the TV line to nextline swinging plus or minus phase burst signals, and/or the plus/minusburst phase portions within each TV line. Therefore the resulting signaltends to produce less hue errors than does the unmodified color stripesignal.

[0060] Variants of the above described methods are illustrated in FIGS.2A and following. FIG. 2A illustrates (in simplified form) thehorizontal sync pulse and color stripe burst of FIG. 1C. The hatchedarea is the color stripe burst area; the individual color burst cyclesare not shown here for simplicity. In the case of FIG. 2A, the entirecolor burst is phase shifted as indicated by the hatching.

[0061] One method to defeat the color stripe process is illustrated inFIG. 2B, wherein a portion (here the right hand or later portion) of thecolor stripe burst is modified to be in correct phase and/or negativecolor stripe burst phase, as illustrated by the absence of hatching. Asdescribed above, it has been found that if about half or more of theduration of the color stripe burst has its phase corrected or isblanked, the color stripe burst is effectively defeated. That is, theNSTC color burst is 8 to 10 cycles long; it has been found thatmodifying 4 to 6 of these cycles is adequate.

[0062]FIG. 2C shows another method to defeat the color stripe process;here the central portion of the color stripe burst is blanked. The firstand second portions are corrected to the correct phase; this shows thatthe entire color stripe burst need not be present in order to achieveproper color functioning of the VCR and/or television set.

[0063]FIG. 2D shows a variant of FIGS. 2B and 2C, where the first andlast portions of the color stripe burst have their phase corrected, butthe central portion remains with the incorrect phase. As shown hereapproximately 30% or 40% of the color burst remains at the incorrectphase but this still effectively defeats the color stripe process.

[0064] In FIG. 2E the entire color stripe burst has been blanked with nosubstitution provided. In this case it has been found that there is noneed for a color burst in each and every video line for effectivefunctioning of most television sets and VCRs.

[0065] In FIG. 2F the first portion of the color stripe burst has beenblanked; instead a few cycles of color burst of correct phase areoverlaid on the actual horizontal sync pulse. Even at this location theywill be detected by the color synchronization circuitry of the TV set orVCR. A portion of the color stripe burst is still present i.e. thecentral portion; the last portion of the color stripe burst has itsphase corrected to be normal.

[0066]FIG. 2G shows a last and obvious variant wherein the entire colorstripe burst has its phase corrected, by replacing or altering the colorstripe burst to be of correct phase.

[0067] Other defeat methods include those that relate to the horizontalsync pulses:

[0068] 11. Replace all correct phase color bursts throughout the TVfield with color bursts having the phase of the color stripe bursts.Then modify each corresponding active horizontal TV line's chroma phaseto equal that of the color stripe bursts. For example, if the colorstripe burst phase is 180° off from the correct color burst phase, thenone modifies the correct color burst phase color burst by 180°. One canalso replace all color bursts with bursts having an arbitrary phase, andthen phase shift the chroma phase in the active portions of the TV linesto be equal to the arbitrary phase.

[0069] This modifying can be done by phase shifting and/or delaycircuits and/or inverting amplifiers. With this modification, the chromaphase in each TV horizontal line is 180° off from that of the modifiedburst as described above. To correct this discrepancy, one then modifieseach of the TV horizontal active lines by phase shifting its chroma by180°. This can be done by switching in a phase shifted or delayedversion of the original video active horizontal TV lines in conjunctionwith the modified color burst. Again one can obtain a copiable recordingby modifying a sufficient number of correct color bursts and phaseshifting a sufficient number of TV horizontal lines.

[0070] 12. Remove the horizontal sync pulse such that the VCR burstdetection circuit (which usually relies upon a preceding horizontal syncpulse) is disabled. One can effectively “remove” horizontal sync pulsesseveral ways. For instance, one can remove the horizontal sync pulsesimmediately preceding at least some locations of the color stripe burst.It has been found that removing e.g. four horizontal sync pulsescoincident with a band of color stripe burst video lines results in acopiable recording without adversely affecting the horizontal linetiming of the VCR. Removal of these horizontal sync pulses can also bedone by narrowing the horizontal sync pulse coincident with the colorstripe burst lines. This narrowing is done until the color stripeeffectiveness is reduced to the point it is possible to make a copiablerecording. As an example, one may reduce the horizontal sync pulses downto 100 nanoseconds width. It has also been found that removing only someof the horizontal sync pulses coincident with the color stripe burstlines reduces the effectiveness of the color stripe signal. For example,every other line where a color striped burst occurs, the horizontal syncpulse is removed from that line.

[0071] 13. DC level shift upward the horizontal sync pulses precedingthe color striped bursts. This causes the VCR's sync separator to failto produce an output in response to these level-shifted horizontalpulses.

[0072] Other methods to effectively remove the horizontal sync pulsesare to black clip or amplitude attenuate them to about 20 IRE or less sothat the VCR's sync separator will not sense these smaller amplitudehorizontal sync pulses, and thus not create a burst sampling pulse, whencolor stripe bursts are present.

[0073] These last two methods may lead to “playability” problems, due tothe missing horizontal sync pulses. “Playability” refers to theresulting video signal including significant visual defects due to“slicing” off of active video as caused by improper horizontal syncpulse separation. This causes some sync separators in televisionsreceivers or VCRs to generate false horizontal synchronizing pulses. Tominimize such playability problems one can:

[0074] Add a pedestal voltage or signal such as a ramp of 0 IRE at thebeginning of the active TV line to about 10 IRE at the end of the TVline to all active TV lines; and/or

[0075] widen all other horizontal sync pulsewidths to about 6microseconds.

[0076] 14. In video lines where color stripe bursts are present, add adelay of about 2 microseconds or more such that the VCR's burst samplingpulse (triggered by the horizontal sync pulse) between the trailing edgeof the horizontal sync pulse and the beginning of the color strip burstmissamples (misses) the delayed color stripe burst.

[0077] 15. Heterodyne the color stripe burst signal into the correctphase by mixing it with a signal such that the resultant has the correctphase.

[0078] 16. Heterodyne the color stripe burst to a new frequency suchthat the VCR will be non-responsive to it. For example, the color stripeburst could be shifted by heterodyning it to a 15 MHz signal or a 2 MHzsignal.

[0079] In any of the above embodiments, one may replace the color phaselock loop with at least one stage of crystal filtering such as a ringingcircuit.

General Circuit

[0080]FIG. 3 shows a block diagram of an apparatus in accordance withthe present invention suitable for carrying out the above-describedmethods for defeating the color stripe process. An input video signal“video in” is typically provided from a cable television source, butpossibly from other sources such as prerecorded video tape. (However,the color stripe process is generally not suitable for pre-recordedvideo tape.) The input video signal is provided to a circuit including acolor stripe location memory 12. This is typically a programmed readonly memory. e.g. an EPROM, which includes data indicating on which ofthe 525 lines of the NTSC television field the color stripe bursts arelocated. This EPROM is programmed prior to assembly of the circuit, andthe knowledge of the location of the color stripe burst is determined byobservation. Therefore it might be determined that the color stripepattern is the commercial embodiment as described above with four videolines having the color stripe burst followed by eight video lineswithout the color stripe burst, etc. The output signals of the colorstripe location from the memory 12 include a line location gate (LLG)signal indicating on which lines the color burst is located. The LLGsignal is thus high for the entire duration of a line having a colorstripe burst.

[0081] A second output signal from the color stripe location memory 12is a pixel location gate (PLG) signal which indicates in exactly whichportions of the color burst are to be modified. The LLG signal is usefulbecause as explained above in certain embodiments of the invention onlya portion of each color burst is modified and other portions are not.Thus typically the PLG signal is high for only a portion of a colorstripe burst, but it may of course be high for the entire duration of acolor stripe burst where it is desired to modify and/or eliminate theentire color stripe burst.

[0082] Again, the data to generate the PLG signal is stored in a part ofmemory 12 which stores enough data to divide up the color stripe burstinto e.g. 20 segments and to modify or not modify each of thosesegments. Since the color burst in NTSC television is eight to tencycles in duration, each of these cycles may be treated individually bythe PLG signal.

[0083] An oscillator 16 provides an output signal having the subcarrierfrequency signal (3.58 MHz for NTSC). This oscillator (timing signalgenerator) may be for instance a phase lock loop, or a crystal filteroscillator, or may derive the subcarrier frequency from the frequency ofthe horizontal sync pulse edges and then multiply the horizontal syncpulse frequency by frequency multipliers or by a phase lock loop tocause the circuit to lock on to the correct color subcarrier frequency.

[0084] A phase detector circuit 18 provides an output signal which iseither logically high or low and is called the color stripe detector(CSD) signal. Thus when the signal is high it indicates that the colorstripe burst has been detected in a particular video line. This CSDdetection signal is useful when the video line locations of the colorstripe bursts are not known. This is typically used where the colorstripe burst locations are dynamic, i.e. not stationary. Thus use of thephase detector is an alternative to the use of the LLG signal and theyare typically not both used in a single circuit. Thus the circuit ofFIG. 3 is a generalized representation of several alternative circuitssharing common elements and shown here as one circuit for purposes ofexplanation.

[0085] The phase detector circuit 18 includes a phase detector, theoutput signal of which is provided to a comparator to compare the phaseof a particular color burst to that of a normal color burst. If thecomparison indicates no difference, then the color stripe detectorsignal is low, i.e. there is no color stripe burst present; if there isa difference, then the color stripe detector signal is a high signalindicating the presence of a color stripe burst.

[0086] The right hand portion of FIG. 3 shows a generic modificationcircuit 22. This circuit 22 may be any one of a number of circuits, eachof which performs one of the types of modification to the video signalas disclosed above and is described in detail hereinafter. In additionto receiving as inputs the indication of the presence of the colorstripe, i.e. either the LLG signal or the CSD signal, and the PLG signalindicating which portions of the color stripe are to be modified as wellas the subcarrier frequency signal, the modification circuit alsoreceives the input video signal.

[0087] The output signal of the modification circuit 22 is a videosignal “video out” which is free of (or has only an attenuated) colorstripe process and hence is copiable by a typical commercially availableVCR.

[0088] As described further below, the modification circuit eitherattenuates or eliminates the color stripe process by direct modificationof the color stripe burst or alternatively operates on the horizontalsync pulse immediately preceding a color stripe burst, and by modifyingthe horizontal sync pulse causes the VCR to ignore the ensuing colorstripe burst.

[0089] Therefore by logically ANDing the output of the phase detector(the CSD signal) or the LLG signal with the PLG signal, one may selectwhich video lines to modify and which portion of each line is to bemodified. As described above, it has been found generally that it isadequate for instance to modify as little as half of a particular colorstripe burst in order to defeat the color stripe process as regards thatcolor stripe burst. Moreover, it has been found experimentally that fortypical commercial embodiments of the color stripe process one maymodify or eliminate as few as one half of the color stripe bursts andstill effectively defeat the color stripe process, i.e. provide acopiable video signal. It is to be understood that herein the terms“copiable” and “recordable” both mean that the resulting video signal,when recorded by a VCR and then played back, provides a viewabletelevision picture without substantial hue defects due to the colorstripe process. Thus these terms refer to effective elimination (defeat)of the effect of the color stripe process in terms of viewability of thevideo signal.

Exemplary Circuits

[0090]FIGS. 4A, 4B, 4C illustrate several exemplary circuits forgenerating the correct color subcarrier frequency and other signals tobe used to replace the color burst signal component in the output videoof the device. FIG. 4C also illustrates a circuit for generating timingsignals to defeat the color stripe process to provide a copiable videosignal therefrom. Thus FIGS. 4A, 4B, 4C and FIGS. 5A, 5B, 6A, and 6Bshow various particular versions of the circuit of FIG. 3.

[0091] Copy protected video from a video source (such as cabletelevision) is conventionally demodulated (not shown) to producebaseband video using well known techniques. This copy protected videousually contains stable video with horizontal and vertical sync andsubcarrier coherency, and includes the color stripe process as describedabove. The copy protection may also include pseudo-sync and AGC pulsepairs as described in the above-referenced U.S. Pat. No. 4,631,603 toRyan and raised back porch pulses as described in U.S. Pat. No.4,819,098 also to John O. Ryan and incorporated herein by reference.These pseudosync and AGC pulse pairs may be removed using the techniquesdescribed in U.S. Pat. 4,695,901 to John O. Ryan and also incorporatedherein by reference. Also incorporated by reference are U.S. Pat. No.5,194,965 to Quan et al., U.S. Pat. No. 5,157,510 to Quan et al., andU.S. patent application Ser. No. 08/062,866 filed by Wonfor et al. whichalso disclose copy protection and defeat techniques relevant to thepresent invention.

[0092] This baseband video in signal (see FIG. 4A) is input toamplifiers A1 and A2. The output of amplifier A1 is coupled to syncseparator U1 which is e.g. National Semiconductor Corp. part numberLM1881 or equivalent. Sync separator U1 generates a frame pulse on line16, a horizontal sync pulse on line 18, and a burst gate signal on line20. Amplifier A2 operates as a sync tip clamping amplifier. One-shot U89generates a sync pulse sample pulse to cause amplifier A2 to be clampedat sync pulses to a specific voltage, i.e. −40 IRE.

[0093] Sync tip clamping is desirable since the input signal may includethe above described pseudo-sync and AGC pulses which would cause backporch clamp circuits to behave incorrectly. The output signal ofAmplifier A2 is about 1 volt peak-to-peak and the blanking level of thevideo output signal of amplifier A2 is clamped to about zero volts.Burst gate inverter U20 is coupled to the control terminal of switchSW1. The clamped video signal from amplifier A2 is coupled to a firstinput of switch SW1 and to the “Clamped Video” output line of FIG. 4C.The second input terminal of SWQ is coupled to ground.

[0094] Switch SW1 gates out the color burst portion of the input videoto produce a gated color burst signal on line 30. Chroma amplifier A3amplifies the gated color burst signal on line 30, and its outputterminal 34 is coupled to a first input terminal of AND gate U100. Theother input terminal of gate U100 is connected to the DS Output terminalof EPROM U5 (see FIG. 4B). EPROM U5 38 is a 525 line EPROM discussedmore fully later; its D5 output terminal provides a signal that istypically high during the active field and low during the verticalblanking interval. It is necessary for the signal at terminal D5 to be“on” during the entire active TV field since it can be programmed to beon during the time of normal color burst signal and/or be low during thetime during the time of color stripe bursts and/or low during verticalblanking interval (VBI) lines without color burst. The output signalfrom gate U100 on line 42 is bursts from the input video, with possiblerestrictions to particular lines in the VBI.

[0095] Color burst phase lock loop U2 has a slow and long time constantin its DC amplifier such that its output signal is phase constant, eventhough color stripe bursts with incorrect phase burst signals arepresent in the video input 42. PLL U2 may alternatively may be a crystalburst continuation oscillator that is injection locked, such as the RCACA1398, or a burst ringing circuit such as a crystal filter. The outputterminal 46 of PLL U2 is coupled to a phase shifter ø2. The outputsignal of phase shifter ø2, on line 50 is a stable 3.58 MHz sine waveCW2 that is used in the circuitry of FIGS. 5A, 5B to produce recordablevideo signals.

[0096] The above discussion assumes that the locations of the colorstripe bursts are known and fixed. If the location of the color stripebursts is moving in line location over time, these color bursts insteadare detected on a line-by-line basis. This detection is done bycomparing the input video burst signal to gate U100 with the outputsignal of circuit U2 using phase detector (PD) U11 (see FIG. 4C). Theoutput signal of phase detector U11 is coupled to 3 MHz low pass filter(LPF) LPF3 to an input terminal of switch SW20. Switch SW20 iscontrolled by an inverse clamp pulse on line 24. Switch SW20 andcapacitor C4 sample and hold the output of the 3 Mhz low pass filterLPF3 during the burst gate interval. The non-inverting input signal toamplifier A4 hence is a line-by-line identification of the burst phase.An incorrect burst phase from a color stripe signal causes a differentvoltage to appear at the input terminal of amplifier A4 than when thecorrect burst phase occurs. Amplifier A4 operates a threshold detectorthat triggers high when color stripe bursts are present. The outputsignal of amplifier A4 hence is a color stripe detection signal (CSD) online 62 that is used in the circuitry of FIGS. 5A, 5B to producecopiable signals.

[0097] A second method to generate a stable color subcarrier is toderive a subcarrier signal from the horizontal sync portion of the videosignal. This method is applicable when there is sync-to-burst coherence,which is the case when the color stripe process is applied in cabletelevision applications. To achieve this, a horizontal sync pulse signalon line 18 from sync separator U1 is coupled to a 45 microsecondnon-retriggerable one shot U3 to eliminate the horizontal sync pulsespresent during the vertical interval and/or the pseudo sync pulses whenboth are in the video input signal.

[0098] The output terminal of one shot U3 (see FIG. 4B) is coupled to afirst input terminal of a 10 bit counter U4. The reset input terminal ofcounter U4 is coupled to a frame pulse output terminal of sync separatorU1 by way of line 16 and a differentiation circuit including capacitorC1 and resistor R1. The output signals of 10 bit counter U4 feed a 10bit bus to EPROM circuit US. EPROM US is programmed to set high or lowlogic levels within the TV frame (525 lines in NTSC). The outputterminals of EPROM US are D0 to D7. The signal on terminal D3 can behigh all the time or high during a portion of the TV field. The signalon terminal D3 controls the tri-state control of the flip-flop U6 Qoutput. One shot U3's output terminal is coupled to the clock inputterminal of phase detector flip-flop U6. Horizontal sync edges from oneshot U3 set flip flop U6, while the output signal of divider U7 resetsflip flop U6. The output terminal of flip flop U6 is coupled to low passfilter and amplifier LPF1 for filtering and amplification (see FIG. 4C).The output of filter LPF1 is coupled to a crystal voltage controlledoscillator VCO operating at 14.318180 MHz.

[0099] As a result of the input signal from filter LPF1, oscillator VCOis locked to the video horizontal sync pulses. The output terminal ofoscillator VCO is coupled to divide-by-4 counter U8 to produce asubcarrier frequency signal on line 76. The divide-by-4 counter U8 isreset at its CLR terminal every frame and results in a 0° or 180°ambiguity in the correct phase of subcarrier frequency on line 76. Tocorrect this, the signal of divide-by-4 counter U8 is phase compared byphase detector U10 with the normal burst of the input by sampling at avideo line known to have a normal burst, i.e. video line 14, and holdingvia capacitor C3. If the phase is correct from counter U8, amplifier A5outputs a low state and the output of exclusive OR gate U9 will notinvert the phase of the output signal of counter U8. If the phase of theoutput signal of counter U8 is incorrect (180°), phase detector (PD) U10supplies a voltage (via low pass filter LPF2 and switch SW10) toamplifier A5 such that the output of A5 amplifier is high. This thencauses the output of XOR gate U9 to invert phase by 180°.

[0100] Switch SW10 is controlled by the signal at terminal D6 of EPROMU5.

[0101] This circuit generates the correct subcarrier phase at the outputterminal of XOR gate U9. The output signal of XOR gate U9 is coupled tophase shifter ø1. The output of ø1 is a 3.58 MHz subcarrier signal CW1on line 94 that is used in the circuitry of FIGS. 5A, 5B to generate oneor more recordable output signals.

[0102] Additional circuitry in FIG. 4C includes 10 bit counter U60, theoutput terminals of which are coupled to horizontal line pixel locationEPROM U70. Individual pixels are located by resetting the 10 bit counterU60 with horizontal rate edge signals from the output terminal of oneshot U3 and clocking 10 bit counter U60 with the output signal ofoscillator VCO. The 10 bit bus output signals of 10 bit counter U60 arecoupled to the address lines of EPROM U70 to generate outputs DD0 TODD7. These outputs (pixel location gate signals) represent pixellocations within the horizontal lines throughout the video field.

[0103] In addition to the FIG. 4C output signals discussed above,several additional output signals from FIG. 4C are used in the circuitryof FIGS. 5A, 5B. A first group of these include: (1) the D0 outputsignal of EPROM U5 which provides an “all locations” indication of colorstripe pulses designated ACSL on line 100; (2) the D1 output signal ofEPROM U5 which provides a “some location” indication of color stripepulses designated SCSL on line 102; and (3) the output signal atterminal D4 of EPROM U5 which provides an “all active field” outputdesignated AFL on line 104. These signals correspond to the linelocation gate signal of FIG. 3.

[0104] Additionally, there is: (1) a horizontal sync HSYNC output signalprovided on line 18 by the horizontal sync output terminal of syncseparator U1; (2) a CLAMPED VIDEO output signal on line 108 provided bythe output terminal of clamp amplifier A2; and (3) a BURST GATE outputsignal provided by a burst gate output terminal 20 of sync separator U1.All of these output signals are used for various parts of the circuitrydescribed in FIGS. 5A, 5B, 6A, 6B.

[0105]FIGS. 5A, 5B and 6A, 6B show various exemplary circuits to use thecolor subcarrier and other signals generated in FIG. 4C for variousmethods to produce a video output signal recordable by a videocassetterecorder. Hence FIGS. 5A, 5B and 6A, 6B are illustrative of variouspossible circuits; an actual circuit hence would only include selectedportions of what is shown in FIGS. 5A, 5B and 6A, 6B.

[0106] The first of these circuits produces a copiable video outputsignal VIDOUT 1, at terminal 200. The user can select a suitablesubcarrier signal generated in FIG. 4C by selecting either the signalCW1 on lines 94 or signal CW2 on line 62 using a jumper JP1. The outputterminal of jumper JP1 is coupled to an attenuator PAD which attenuatesthe selected subcarrier signal. Clamped video on line 108 and attenuatedsubcarrier from the attenuator PAD are coupled to the first and secondinputs of switch SW100. Switch SW100 is controlled by an output terminalof AND Gate U305, with one input terminal of gate U305 coupled to outputline DDo of EPROM U5 carrying a burst gate signal of a width dependingof the programming of the EPROM U5. The other input terminal of AND gateU305 is selectively connected to the ACSL signal on line 100, the SCSLsignal on line 102 or the CSD signal on line 62 using a combination ofjumper JP2 and jumper JP3.

[0107] This circuit permits the user to select video lines of therecordable video output VIDOUT 1 at terminal 200 which are to receivereplacement color burst signals. If the ACSL signal is selected, therecordable video output VIDOUT 1 includes corrected color bursts on allvideo lines where color stripe burst are known to be. If the SCSL signalis selected, the recordable video output VIDOUT 1 includes correctedcolor bursts on a sufficient number of video lines to substantiallyreduce or nullify the effects of the color strip process on the recordedvideo.

[0108] The ACSL signal is preprogrammed and indicates the video lineswhich as determined by observation have in turn been preprogrammed bythe color stripe generator. (The color stripe generator is theapparatus, not illustrated here, that puts the color stripe process intothe video signal.) In some cases it is not known which lines have beenpreprogrammed, and then the CSD Signal is used to determine which videolines need to have color burst corrected. If the CSD signal is selectedusing jumper JP3 to drive AND Gate U305, the circuit replaces all or atleast a majority of the color stripe burst in the recordable videooutput VIDOUT 1, such that the effects of the color stripe bursts areessentially nullified.

[0109] In each of the above techniques, the signal on the DDo outputterminal of EPROM U5 is programmed to switch in enough of a portion ofthe correct burst in each line to substantially reduce or nullify thecolor stripe process.

[0110] A second circuit produces a recordable video output signal VIDOUT2, at terminal 214. This circuit switches in a phase shifter during thevideo lines where a color stripe burst is known, to shift the knownphase error of the color stripe burst. A first input signal to switchSW102 is clamped video on line 108 which contains color stripe burstswith a known value of phase shifted color burst signals. The secondinput signal to switch SW102 is the output signal of phase shifter ø3,which is a phase shifted version of the clamped video signal. Thecontrol terminal of switch SW102 is connected to the output terminal ofAND gate U305 which provides the same switching pulses as does controlswitch SW100. These pulses permit selection of enough of a correctedcolor burst of essentially the correct phase in each line tosubstantially reduce or nullify the color stripe process.

[0111] A third circuit for providing a copiable video output signal addsin a large amplitude of a correct burst signal to the color stripedvideo and then attenuates the resultant burst to nominal burst levels.This circuit is accomplished as follows.

[0112] The clamped video signal on line 108 is coupled to a first inputterminal of summing amplifier A36. The color subcarrier signal selectedby jumper JP1, either signal CW1 or CW2, via attenuator PAD is coupledto an input terminal of switch SW101. Switch SW101 selects theattenuated color subcarrier, that is at normal burst amplitude, duringthe times determined by EPROM U305 as discussed above. The outputterminal of switch SW101 is coupled to amplifier A35, which is a 10×amplifier producing a color subcarrier burst signal 10 times the normalamplitude.

[0113] This amplified color burst signal is coupled to a second inputterminal of summing amplifier A36, where it is summed with the clampedvideo signal on line 108 containing color stripe bursts. The outputterminal of summing amplifier A36 is coupled to a switched attenuatorincluding resistor R9, resistor R10 and switch SW104. Switch SW104 iscontrolled by the burst gate signal from sync separator U1 at line 20 online 110. Closing switch SW104 230 attenuates the output signal ofamplifier A36 during the duration of the burst gate signal. This ineffect “swamps” any color stripe bursts present in the input videosignal. The output of the switched attenuator is coupled to amplifierA44, which is a unity gain amplifier, to provide copiable video outputVIDOUT 3 at terminal 218. Note that switch SW104 which causes the burstamplitude reduction can be closed during some or all of the color stripelines and also during a portion of the color burst in each line toproduce a recordable (copiable) signal. Note also that the addition of alarge amplitude color burst via amplifier A36 followed by burstamplitude reduction can be done a majority of the video lines in a videofield to produce a recordable signal.

[0114] A fourth technique for providing a copiable video signal includesremoving the color stripe burst and/or the horizontal sync pulsespreceding the color stripe bursts. By doing this, the recording VCR willnot try to heterodyne correct the color stripe burst line with anincorrect phase burst signal. All or some of the lines with color stripebursts that have horizontal sync pulses or color stripe bursts blankedout results in a recordable copy. It should be noted that only some ofthe relevant horizontal sync pulses are narrowed or only some of therelevant color stripe bursts are narrowed to produced a recordableoutput.

[0115] A circuit for implementing this fourth technique is as follows.Clamped video on line 108 is coupled to resistor R107 which in turn iscoupled to unity gain amplifier A55. A combination of NAND Gate U110,AND Gate U120, jumper JP5, jumper JP4, and OR Gate U130 provides thetiming signals to blank out color stripe burst and/or the horizontalsync pulses preceding the color stripe bursts. Switch SW103 grounds theinput terminal of unity gain amplifier A55 whenever the selected pulsesor burst intervals are selected by the elements outlined above. Thetiming components described above may blank out the horizontal pulses orcolor stripe burst signals during all or only during a portion of acolor stripe burst period or its accompanying horizontal sync pulse. Theoutput terminal of unity gain amplifier A55 provides recordable videooutput VIDOUT 4 at terminal 220.

[0116]FIGS. 6A, 6B illustrate other circuits to use the color subcarrierand pulses generated by the circuitry of FIG. 4C to produce recordable(copiable) video output signals.

[0117] A fifth technique for producing a recordable video signaleliminates the effect of the horizontal sync pulses associated with thecolor stripe bursts, using level shifting the horizontal sync pulses.The effects of level shifting are described in “Method and Apparatus ForDisplaying Anti-Copy Protection In Video Signals”, U.S. Pat. No.5,194,965 issued to Quan et al. on Mar. 16, 1993, and which isincorporated by reference.

[0118] This fifth technique is accomplished as follows. Clamped video online 108 from FIG. 4C is coupled to a first input terminal of summingamplifier A99. The other input terminal of amplifier A99 is connected toan output terminal of gate U120 which may contain a positive goinghorizontal sync pulse coincident with a color stripe burst. The outputterminal of gate U120 may also carry part of a horizontal sync pulsecoincident with some of the color stripe bursts. Which lines areaffected is a function of the timing described in the fourth techniqueabove. Thus the level shift of the horizontal sync pulse may occur onlyin a portion of a specific line or in the specific lines having colorbursts. The amount of level shifting may adjusted to produce the amountneeded to produce a recordable video output. The output of terminalsumming amplifier A99 250 provides the recordable video output signalwith level shifted horizontal sync pulses.

[0119] A sixth techniques for producing a recordable video signal is toeliminate the effect of the horizontal sync pulses associated with thecolor stripe bursts by clipping the associated horizontal sync pulses.

[0120] The sixth technique is accomplished as follows. A sync clippingcircuit includes amplifier A91, transistor QBCL and resistor RS.Amplifier A91 inverts and attenuates the logic level of the gate U120output signal described above. The output signal of amplifier A91 istypically about zero IRE to −10 IRE. When the clamped video signal iscoupled through resistor Rs, its horizontal sync pulses will be clippedto −10 IRE during a portion of or all the color stripe burst lines,depending upon the logic level output of gate U120. In addition, eachhorizontal sync pulse may be clipped for its full duration or part ofits duration. The amount of clipping duration depends on the ability tomake a recordable copy. Amplifier A77 outputs the recordable videosignal VIDOUT 6 with clipped horizontal synchronizing signals.

[0121] A seventh technique for producing a recordable video output is toeliminate the effect of the horizontal sync pulses associated with thecolor stripe bursts by widening those horizontal sync pulses.

[0122] This is accomplished as follows. The clamped video signal on line108 is coupled to a first input terminal of switch SW124. The secondinput terminal of switch SW124 is coupled to a widened horizontal syncsignal which is provided by the DD3 output terminal of EPROM U70. SwitchSW124 is controlled by the signal at the output terminal of AND GateU123 that ANDs the horizontal blanking signal at terminal DD4 of EPROMU70 and the active field lines output signal on line 64.

[0123] This seventh technique uses the output signal of gate U120 tocontrol switch SW124. The resultant signal on any video lines determinedto have color stripe burst signals is no color burst, because thewidened horizontal sync eliminates the color burst. Unity gain amplifierA88 couples the recordable video output with the widened horizontalsynchronizing signals to the VCR.

[0124]FIG. 7 shows a circuit to improve playability in conjunction withelimination of horizontal sync pulses, by adding an offset voltage tovideo that has the horizontal sync pulses eliminated. This added offsetvoltage allows the sync separator in a TV or VCR not to slice at videolevels caused by missing horizontal sync pulses.

[0125] To generate a voltage pedestal during the active lines of theactive field, the active horizontal line pixel locations indicated by asignal at terminal DD5 of EPROM U70 are logically combined by AND gateU467 with the signal at terminal D4, which indicates the active fieldline locations. The output of gate U467 is provided to a current mirrorincluding transistors Q_(A) and Q_(B) via resistor Rped. The collectorof transistor Q_(A) feeds a current mirror including transistors Q_(D)and Q_(C). The collector of transistors Q_(C) then injects a pedestalcurrent into resistor Rss to add a pedestal voltage to the clamped videoinput. The output signal (via a buffer amplifier A40) then feeds intothe various horizontal sync pulse clipping, shifting or blankingcircuits described herein.

[0126] An eighth technique for producing a recordable video output is todelay the color stripe burst so as to be out of the range of the burstdetection circuitry, to effectively cause the color burst to “drop out.”

[0127] The technique is accomplished as follows. Clamped video on line108 is coupled to a chroma band pass filter including resistor Ro,inductor L4 and capacitor C4 and to a first input terminal of switchSW123. The output signal of the chroma pass filter is buffered andamplified by amplifier A98. The output terminal of amplifier A98 iscoupled to delay line 276 which delays the chroma output of the bandpass filter by e.g. 2 microseconds. The output terminal of the delayline 276 is coupled to a second input terminal of switch SW123. SwitchSW123 is controlled by the output signal of AND Gate U278. Horizontalsync pulses from sync separator U1 are coupled to the input terminal ofone-shot U505 which generates a 4 microsecond pulse triggered by thetrailing edge of the horizontal sync input signal. AND Gate U278generates a control signal for switch SW123 from a logical combinationof the output signal of one-shot U505 and the D1 terminal output signalof EPROM US which is a signal representing some locations of colorstripe Lines (SCSL), as described above.

[0128] The output signal of switch SW123 has a delayed color burst onvideo lines having color stripe bursts. The delayed color burst is notdetected by a VCR. Therefore the VCR is not responsive to the lineshaving a color stripe burst. Amplifier A97 buffers the output signal ofswitch SW123 and provides an output signal with delayed color stripebursts that is recordable.

[0129] A ninth technique for producing a recordable video signal usessignal multiplying (heterodyning) to shift the color stripe burst phaseto be correct and/or to shift the color stripe bursts out of thefrequency range of the burst detection circuitry, to effectively causethe VCR color burst to “drop out”.

[0130] Clamped video on line 108 is coupled to a first input terminal ofsignal multiplier 282, the second input terminal of is connected to a 1volt DC signal most of the time, as controlled by signal SW122. Tocontrol the color stripe burst phase, switch SW122 couples via jumperJP207 the cos(2πf_(sc)t+ø) signal from FIG. 4C generated by frequencydouble amplifier A10 and phase shifter ø4, or to shift the color stripeburst out of frequency range, a cos(2π18.6×10⁶t) signal from anyoscillator source is used to heterodyne the color stripe bursts. SwitchSW122 is controlled by the output of AND gate U305.

[0131] Because of the 1 volt DC at switch SW122 and the control signalfrom gate U305, the output signal of multiplier 282 is “transparent”(equal to the signal on line 108) during most of the time. During thetime of color stripe burst signals as determined by the output signal ofgate U305 however, the output signal of multiplier 282 is equal to colorstripe frequency plus a corrected color burst phase angle orcos(2πf_(sc)t+ø_(A)) and three times the color burst frequency plusanother phase angle or cos(2π3f_(sc)t+ø_(B)). The output multiplier iscoupled to low pass filter LPF4. Low pass filter LPF4 has a cut offfrequency of about 5 MHz so that the three times color burst frequencyis eliminated. The output signal of low pass filter LPF4 is coupled toamplifier A74 that buffers the output signal of low pass filter LPF4 andprovides an output with color stripe burst that hence are recordable.

[0132] If the second input terminal of switch SW122 is coupled to an18.6 MHz sine wave, and low pass filter LPF4 is designed to cut off at16 MHz, the output signal of multiplier 282 during the color stripeburst time, as determined by the output of gate U305, will have burstfrequencies of about 15 MHz and 22 MHz. Such a LPF4 will pass throughthe 15 MHz burst during the color stripe times. When this signal iscoupled to a VCR, the VCR's chroma input filter will be unresponsive tothe 15 MHz since it is expecting a 3.58 MHz burst (and filters outhigher frequency). Thus during the lines with color stripe bursts, thecolor stripe burst is defeated.

[0133]FIG. 8 shows a circuit for carrying out the above described methodof replacing correct phase color bursts with color stripe bursts andthen modifying the chroma phase to that of the color stripe bursts. Theclamped video signal is provided to phase shifter U75, which shifts thephase by an amount equal to the difference between that of the colorstripe bursts and the correct color burst phase. Switch SW124,controlled by the burst gate signal, outputs the clamped video having ineach line of the TV field a color burst having the phase of the colorstripe burst. Similarly controlled switch U126 then in turn outputs theclamped video having each TV horizontal line phase shifted (includingthe active chroma) to match the phase shift of the color stripe burst,which signal is copiable.

[0134]FIG. 9 illustrates a circuit for subcarrier regeneration withoutthe use of a phase lock loop or a voltage control oscillator, for use inconjunction with the above described circuitry in one embodiment of theinvention. The output signal from one shot U3 of FIG. 4B is provided toa 32 μsec one shot U60, the output signal of which is the equivalent ofthe horizontal line frequency i.e. a square wave with the horizontalline frequency. This signal is provided to a band pass filter BPF3 whichpasses a 13th harmonic of horizontal sync. Thus this signal which is 13times the horizontal frequency is fed to a limiter amplifier A47 whichin turn is connected to the input terminal of a bandpass filter BPF4which passes the seventh harmonic of the 13 times the horizontalfrequency. This frequency, which is seven times the 13th harmonic of thehorizontal frequency, is provided to a second limiter amplifier A48which in turn is connected to the input terminal of a band pass filterBPFG which passes a band of a fifth harmonic of seven times the 13thharmonic of the horizontal frequency, and which in turn is connected toanother limiter amplifier A50 which connects to the clock terminal of adivide by 2 counter U68. The noninverting Q output terminal of counterU68 provides a signal of 3.57954 MHz which of course is exactly thedesired subcarrier frequency for NTSC television. This signal in turn isthe first input to a color phase identification circuit U70 (similar tothat shown in FIG. 4C) which provides as an output signal thereof (inresponse to the frame pulse provided at the other input terminal) thedesired correct color phase and frequency subcarrier for each TV field.A similar scheme to regenerate color subcarrier can be done via verticalsync signals through frequency multipliers and/or (crystal) phase lockloop circuits.

[0135] This disclosure is illustrative and not limiting; furthermodifications will be apparent to one skilled in the art and areintended to fall within the scope of the appended claims.

We claim:
 1. A method of removing phase modulation induced in the colorburst of a video signal, the phase modulation being for inhibiting themaking of acceptable video recordings of the video signal, the methodcomprising the steps of: determining in which lines of the video signalthe induced phase modulation is present; and modifying the induced phasemodulation in at least some of those lines whereby an acceptable videorecording of the video signal can be made.
 2. The method of claim 1,wherein the step of determining comprises the steps of: storing data ina memory indicating in which predetermined lines of the video signal theinduced phase modulation is present; and accessing the memory.
 3. Themethod of claim 1, wherein the step of determining comprises the step ofsensing a presence of the induced phase modulation line-by-line.
 4. Themethod of claim 3, wherein the step of sensing comprises the steps of:for each video line, comparing a phase of the color burst of that lineto a known phase; and if the phase of the color burst differs from theknown phase, providing a signal in response indicating the presence ofthe induced phase modulation.
 5. The method of claim 1, wherein the stepof modifying includes modifying less than all of the lines in which theinduced phase modulation is present, but sufficient of the lines so thatthe acceptable video recording can be made.
 6. The method of claim 5,wherein the step of modifying includes: generating a color burstfrequency; replacing at least a part of the color burst in less than allof the lines with the generated color burst frequency; and resetting aphase of the generated color burst frequency at intervals of a multipleof two fields of the video signal.
 7. The method of claim 1, wherein thestep of modifying comprises the steps of: generating a signal having thecolor burst frequency by multiplying a frequency of the horizontal syncpulses to the video signal; and replacing at least part of the colorburst in at least some of the lines with the generated signal.
 8. Themethod of claim 1, wherein the step of modifying comprises phaseshifting the color burst.
 9. The method of claim 1, wherein the step ofmodifying comprises: generating a phase shifted color burst signal; andinserting the generated color burst into the video signal.
 10. Themethod of claim 11 wherein the step of modifying comprises: delaying atleast a portion of the active video portion of each line, therebymodifying the effect of the induced phase modulation.
 11. The method ofclaim 10, wherein the delayed portion of the active video portion is achroma signal.
 12. The method of claim 6, wherein the step of generatingcomprises providing a signal from a signal source.
 13. The method ofclaim 1, wherein the step of modifying includes the steps of:determining an amount of phase error in each line; adding to the line acolor burst of a phase opposite to that of the determined phase error;and after the steps of adding, attenuating an amplitude of the colorburst portion of the signal to a normal level.
 14. The method of claim1, wherein the step of modifying comprises the steps of: generating acolor burst frequency having an amplitude greater than that of a normalcolor burst; adding the generated color burst frequency to each line;and after the step of adding, attenuating an amplitude of the colorburst portion of the line to a normal level.
 15. The method of claim 1,wherein the step of modifying includes the steps of: generating a firstcolor burst signal having a phase opposite to that of the induced phasemodulation; generating a second color burst signal having a correctphase; and adding the first and second color burst signals to the colorburst portion of each video line.
 16. The method of claim 1, wherein thestep of modifying comprises the steps of: measuring an amount of theinduced phase modulation for a line, relative to a normal color burst;generating a color burst frequency signal having a phase opposite to thedetermined amount of induced phase modulation; and adding the generatedcolor burst frequency to an immediately following line, thereby to causea swinging phase of the color burst from one line to the immediatelyfollowing line.
 17. The method of claim 14, wherein the steps ofmeasuring and adding are undertaken only for every other line having aninduced phase modulation.
 18. The method of claim 1, wherein the step ofmodifying includes attenuating a color burst portion of the signal. 19.The method of claim 1, wherein the step of modifying includeseliminating.
 20. The method of claim 1, wherein the step of modifyingincludes: in those lines of the video signal in which the induced phasemodulation is not present, inducing a phase modulation; and modifying aphase of a chroma in the video signal to equal that of the induced phasemodulation.
 21. The method of claim 1, wherein the step of modifyingincludes selecting a sufficient number which is less than all of thelines for modifying to allow the acceptable video recording to be made.22. The method of claim 1, wherein the steps of modifying includemodifying only a portion of a color burst in any particular video line,thereby leaving a remaining portion of the color burst with the inducedphase modulation.
 23. The method of claim 1, wherein the step ofmodifying includes attenuating a horizontal synchronization pulsepresent in the at least some of the lines.
 24. The method of claim 23,wherein the step of. attenuating includes removing the horizontalsynchronization pulse.
 25. The method of claim 23, wherein the step ofattenuating includes narrowing the horizontal synchronization pulse. 26.The method of claim 23, wherein the step of attenuating includes levelshifting the horizontal synchronization pulse.
 27. The method of claim23, wherein the step of attenuating includes amplitude attenuating thehorizontal synchronization pulse.
 28. The method of claim 1, furthercomprising the steps of: adding a pedestal signal to all active videolines in the video signal; and extending a duration of horizontalsynchronization pulses other than those subject to the step ofattenuating, to at least 6 μsec.
 29. The method of claim 23, wherein thestep of modifying comprises delaying the line by at least 2 μsec. 30.The method of claim 23, wherein the step of modifying comprises alteringa frequency of the induced phase modulation to be different than that ofa subcarrier frequency of the color burst.
 31. The method of claim 23,wherein the step of modifying comprises heterodyning at least a portionof the induced phase modulation to a normal color burst phase.
 32. Anapparatus for removing phase modulation induced in the color burst of avideo signal for inhibiting the making of acceptable video recordings ofthe video signal, the apparatus comprising: a color burst locationindicator circuit; and a video line modifier operatively connected toreceive an indicator signal from the color burst location indicatorcircuit.
 33. The apparatus of claim 32, wherein the indicator signalindicates in which lines the induced phase modulation is present. 34.The apparatus of claim 33, wherein the indicator circuit includes amemory in which is stored data indicating in which lines the inducedphase modulation is present.
 35. The apparatus of claim 33, wherein theindicator circuit includes a phase modulation sensing circuit.
 36. Theapparatus of claim 35, wherein the phase modulation sensing circuitcomprises: a timing circuit generating a timing signal having aparticular phase; and a phase comparator connected to receive the timingsignal and the color burst portion of the video signal.
 37. Theapparatus of claim 32, wherein the modifier includes means for modifyingless than all of the lines in which the induced phase modulation ispresent, but sufficient of the lines so that the acceptable videorecording can be made.
 38. The apparatus of claim 32, wherein themodifier includes: a color burst frequency generator; means forreplacing at least a part the color burst in less than all of the lineswith the generated color burst frequency; and means for resetting aphase of the generated color burst frequency at intervals of a multipleof two fields of the video signal.
 39. The apparatus of claim 32,wherein the modifier includes: a color burst generator which multipliesa frequency of the horizontal sync pulses to generate a color burstfrequency; and means for replacing at least part of the color burst inat least some of the lines with the generated frequency.
 40. Theapparatus of claim 32, wherein modifier induces a color burst phaseshifter.
 41. The apparatus of claim 32, wherein the modifier comprises:a phase shifted color burst signal generator; and means for inserting agenerated color burst into the video signal.
 42. The apparatus of claim32, wherein the modifier includes a delay element connected for delayingat least a portion of the active video portion of each line, therebymodifying the effect of the induced phase modulation.
 43. The apparatusof claim 42, wherein the delayed portion of the active video portion isa chroma signal.
 44. The apparatus of claim 38, wherein the generatorcomprises a timing signal generator.
 45. The apparatus of claim 32,wherein the modifier includes: means for determining an amount of phaseerror in each line; means for adding to the line to the line a colorburst of a phase opposite to that of the determined phase error; and anattenuator which attenuates an amplitude of the color burst portion ofthe signal to a normal level.
 46. The apparatus of claim 32, wherein themodifier comprises: a generator which generates a color burst frequencyhaving an amplitude at least three times that of a normal color burst;means for adding the generated color burst frequency to each line; andan attenuator connected to attenuate an amplitude of the color burstportion of the line to a normal level.
 47. The apparatus of claim 32,wherein the modifier includes of: a generator which generates a firstcolor burst signal having a phase opposite to that of the induced phasemodulation; a second generator which generates a second color burstsignal having a correct phase; and means for adding the first and secondcolor burst signals to the color burst portion of each video line. 48.The apparatus of claim 32, wherein the modifier comprises of: means formeasuring an amount of the induced phase modulation for a line, relativeto a normal color burst; a generator which generates a color burstfrequency signal having a phase opposite to the determined amount ofinduced phase modulation; and means for adding the generated color burstfrequency to an immediately following line, thereby to cause a swingingphase of the color burst from one line to the immediately followingline.
 49. The apparatus of claim 48, wherein the means for measuring andthe means for adding operate only for every other video line having aninduced phase modulation.
 50. The apparatus of claim 32, wherein themodifier includes a color burst attenuator.
 51. The apparatus of claim32, wherein the modifier eliminates the color burst.
 52. The apparatusof claim 32, wherein the modifier includes: a phase shifter for shiftinga phase of color burst in the video signal; a first switch connected tothe phase shifter, thereby providing an output signal having in eachvideo line the induced phase modulation; and a second switch connectedto an output terminal of the first switch, thereby providing a phaseshifted video signal.
 53. The apparatus of claim 32, wherein themodifier includes means for selecting a sufficient number of the linesto allow the acceptable video recording to be made.
 54. The apparatus ofclaim 32, wherein the modifier includes a horizontal synchronizationpulse attenuator.
 55. The apparatus of claim 54, wherein the attenuatorremoves the horizontal synchronization pulse.
 56. The apparatus of claim54, wherein the attenuator narrows the horizontal synchronization pulse.57. The apparatus of claim 54, wherein the attenuator level shifts thehorizontal synchronization pulse.
 58. The apparatus of claim 54, whereinthe attenuator amplitude attenuates the horizontal synchronizationpulse.
 59. The apparatus of claim 54, further comprising: means foradding a pedestal signal to all active video lines in the video signal;and means for extending a duration of horizontal synchronization pulses,other than those subject to attenuation, to at least 6 μsec.
 60. Theapparatus of claim 32, wherein the modifier comprises a delay elementwhich delays the video line by at least 1 μsec.
 61. The apparatus ofclaim 32, wherein the modifier comprises a frequency modifier whichalters a frequency of the induced phase modulation to differ from thatof a subcarrier frequency of the color burst.
 62. The apparatus of claim32, wherein the modifier comprises a heterodyne circuit whichheterodynes at least a portion of the induced phase modulation to anormal color burst phase.